Actuation System and Lithographic Apparatus

ABSTRACT

Actuation systems and lithographic apparatus which address the issue of uncontrolled return of common mode currents are provided. In a main an embodiment such systems aim to prevent the occurrence of corona and discharge between high voltage electric cables in low pressure environments. An exemplary actuation system comprises an actuator module, a power source and power transmission cables. The actuator module includes an electrical motor and a first plurality of shielded cables configured to connect to the electrical motor at one end. The actuator module is located in a low pressure environment and each shield of the first plurality of cables is grounded. The transmission cables electrically connect the first plurality of cables with power supply, and comprise an extra cable which is configured to connect each shield of the first plurality of cables with the first extra cable, via a choke so as to provide a return path for common-mode currents.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit under 35 U.S.C. §119(e) to U.S.Provisional Patent Application No. 61/419,446, filed Dec. 3, 2010, whichis incorporated by reference herein in its entirety.

BACKGROUND

1. Field of the Invention

The present invention relates generally to a lithographic apparatus, andmore particularly to an actuation system and a lithographic apparatushaving the actuation system.

BACKGROUND ART

A lithographic apparatus is a machine that applies a desired patternonto a substrate, usually onto a target portion of the substrate. Alithographic apparatus can be used, for example, in the manufacture ofintegrated circuits (ICs). In that instance, a patterning device, whichis alternatively referred to as a mask or a reticle, may be used togenerate a circuit pattern to be formed on an individual layer of theIC. This pattern can be transferred onto a target portion (e.g.,comprising part of, one, or several dies) on a substrate (e.g., asilicon wafer). Transfer of the pattern is typically via imaging onto alayer of radiation-sensitive material (resist) provided on thesubstrate. In general, a single substrate will contain a network ofadjacent target portions that are successively patterned. Knownlithographic apparatus include so-called steppers, in which each targetportion is irradiated by exposing an entire pattern onto the targetportion at one time, and so-called scanners, in which each targetportion is irradiated by scanning the pattern through a radiation beamin a given direction (the “scanning”-direction) while synchronouslyscanning the substrate parallel or anti parallel to this direction. Itis also possible to transfer the pattern from the patterning device tothe substrate by imprinting the pattern onto the substrate.

Some moving parts of the lithography apparatus are powered by a highvoltage power supply. Furthermore, for some lithographic processes,parts of the lithography apparatus are kept at very low pressure. InExtreme Ultraviolet (EUV) lithography, the lithography process isperformed at very low pressure in order to decrease the absorption ofthe EUV radiation by air. In particular, at very low pressure, a highvoltage power supply may be used to power any actuators that are used toposition the table on which the substrate is placed, any so-calledblades that block a portion of the projection beam or any clamps thathold the mask or the substrate to a table that may be part of thelithography apparatus. Due to the fact that high voltage is used, and inparticular because the components are situated in a very low-pressureenvironment, there is a problem that electrical breakdown may occur(Paschen effect). The possibility of electrical breakdown limits thevoltage of the power lines and presents a safety hazard and a lifetimeissue. If a full insulation breakdown occurs, it can pollute surfaces ofoptical components, create electromagnetic interference that disturbssensitive electronics, cause severe machine damage and present a humansafety hazard. Even with partial discharges (ionization corona effect),part of the power line insulation material will be gradually broken downinto gaseous form which can also cause pollution of surfaces of opticalcomponents and will cause electromagnetic interference to sensitiveelectronics.

Another issue is that of the uncontrolled return of common modecurrents. Common mode currents arise from motion control systems withelectric motors (e.g., Wafer Stage). Measurements have shown that theresolution of sensor systems in the machine is deteriorated due to thesecommon mode currents, which interfere with the sensor systems.

SUMMARY

The following presents a simplified summary of the one or moreembodiments in order to provide a basic understanding of suchembodiments. This summary is not an extensive overview of allcontemplated embodiments, and is intended to neither identify key orcritical elements of all embodiments nor delineate the scope of any orall embodiments. Its sole purpose is to present some concepts of one ormore embodiments in a simplified form as a prelude to the more detaileddescription that is presented later.

In accordance with one or embodiments and corresponding disclosurethereof, various aspects are described in connection with providing anactuation system with high voltage electric cables in low pressureenvironments to prevent the occurrence of corona between the cableswhile also preventing uncontrolled return of common mode currents.

According to one embodiment of the present invention, there is providedactuator system comprising an actuator module comprising at least oneactuator and actuator cables configured to connect the at least oneactuator to the outside of the actuator module, a power supply forproviding power to the at least one actuator, and transmission cablesfor connecting the power source to the actuator cables. There isprovided a common mode signal return conductor from the at least oneactuator module to the power supply.

According to a further embodiment of the present invention, there isprovided a feed-through connection for providing a hermetic electricalconnection between regions having different atmospheric pressurescomprising, one or more feed-through conductors, each of which isconfigured at each end to connect to an electrical cable, and one ormore auxiliary feed-through conductors, each of which is insulated fromthe one or more main feed-through conductors, the feed-throughconnection being configured at one end to provide for an electricallyconductive path from an electrically conductive shielding of at leastone of the electrical cables to at least one of the one or moreauxiliary feed-through conductors.

According to a further embodiment of the present invention, there isprovided lithographic apparatus, comprising: a substrate tableconfigured to hold a substrate, a support constructed to support apatterning device, the patterning device being capable of imparting theradiation beam with a pattern in its cross-section to form a patternedradiation beam, and an actuation system of the first embodiment, beingconfigured to actuate the support, the substrate table, and/or any otherfeature of the lithographic apparatus. The lithographic apparatus mayalso comprise a reticle clamp holding a reticle and a shutter to controlthe light path.

One or more embodiments of the present invention are directed tolithography systems and sub-system including the actuation system.

Further features and advantages of the invention, as well as thestructure and operation of various embodiments of the invention, aredescribed in detail below with reference to the accompanying drawings.It is noted that the invention is not limited to the specificembodiments described herein. Such embodiments are presented herein forillustrative purposes only. Additional embodiments will be apparent topersons skilled in the relevant art(s) based on the teachings containedherein.

BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES

The accompanying drawings, which are incorporated herein and form partof the specification, illustrate the present invention and, togetherwith the description, further serve to explain the principles of theinvention and to enable a person skilled in the relevant art(s) to makeand use the invention.

FIG. 1 depicts an exemplary lithographic apparatus according to anembodiment of the invention.

FIG. 2 depicts an exemplary beam interceptor connected to an actuationsystem according to an embodiment of the invention.

FIGS. 3 a and 3 b depict an exemplary actuation system according to twoembodiments of the invention.

FIG. 4 depicts an exemplary cross-sectional view of a cable used in theactuator module.

FIGS. 5 a and 5 b depict a vacuum wall feedthrough device according toan embodiment of the invention.

FIG. 6 a depicts an exemplary spring configuration for the feedthroughdevice of FIGS. 5 a and 5 b when used in the system of FIG. 3 a.

FIG. 6 b depicts an exemplary spring configuration for the feedbackdevice of FIGS. 5 a and 5 b when used in the system of FIG. 3 b.

The features and advantages of the present invention will become moreapparent from the detailed description set forth below when taken inconjunction with the drawings, in which like reference charactersidentify corresponding elements throughout. In the drawings, likereference numbers generally indicate identical, functionally similar,and/or structurally similar elements. The drawing in which an elementfirst appears is indicated by the leftmost digit(s) in the correspondingreference number.

DETAILED DESCRIPTION

This specification discloses one or more embodiments that incorporatethe features of this invention. The disclosed embodiment(s) merelyexemplify the invention. The scope of the invention is not limited tothe disclosed embodiment(s). The invention is defined by the claimsappended hereto.

The embodiment(s) described, and references in the specification to “oneembodiment,” “an embodiment,” “an example embodiment,” etc., indicatethat the embodiment(s) described may include a particular feature,structure, or characteristic, but every embodiment may not necessarilyinclude the particular feature, structure, or characteristic. Moreover,such phrases are not necessarily referring to the same embodiment.Further, when a particular feature, structure, or characteristic isdescribed in connection with an embodiment, it is understood that it iswithin the knowledge of one skilled in the art to effect such feature,structure, or characteristic in connection with other embodimentswhether or not explicitly described.

Embodiments of the invention may be implemented in hardware, firmware,software, or any combination thereof. Embodiments of the invention mayalso be implemented as instructions stored on a machine-readable medium,which may be read and executed by one or more processors. Amachine-readable medium may include any mechanism for storing ortransmitting information in a form readable by a machine (e.g., acomputing device). For example, a machine-readable medium may includeread only memory (ROM); random access memory (RAM); magnetic diskstorage media; optical storage media; flash memory devices; and others.Further, firmware, software, routines, instructions may be describedherein as performing certain actions. However, it should be appreciatedthat such descriptions are merely for convenience and that such actionsin fact result from computing devices, processors, controllers, or otherdevices executing the firmware, software, routines, instructions, etc.

Before describing such embodiments in more detail, however, it isinstructive to present an example environment in which embodiments ofthe present invention may be implemented.

FIG. 1 schematically depicts an exemplary lithographic apparatusaccording to one embodiment of the invention. The apparatus comprises anillumination system (illuminator) IL configured to condition a radiationbeam B (e.g., UV radiation or EUV radiation), a support structure (e.g.,a mask table) MT constructed to support a patterning device (e.g., amask) MA and connected to a first positioner PM configured to accuratelyposition the patterning device in accordance with certain parameters, asubstrate table (e.g., a wafer table) WT constructed to hold a substrate(e.g., a resist coated wafer) W and connected to a second positioner PWconfigured to accurately position the substrate in accordance withcertain parameters, and a projection system (e.g., a refractiveprojection lens system) PS configured to project a pattern imparted tothe radiation beam B by patterning device MA onto a target portion C(e.g., comprising one or more dies) of the substrate W.

The illumination system may include various types of optical components,such as refractive, reflective, magnetic, electromagnetic, electrostaticor other types of optical components, or any combination thereof, fordirecting, shaping, or controlling radiation.

The support structure supports, i.e., bears the weight of, thepatterning device. It holds the patterning device in a manner thatdepends on the orientation of the patterning device, the design of thelithographic apparatus, and other conditions, such as for examplewhether or not the patterning device is held in a vacuum environment.The support structure can use mechanical, electrostatic or otherclamping techniques to hold the patterning device. The support structuremay be a frame or a table, for example, which may be fixed or movable asrequired. The support structure may ensure that the patterning device isat a desired position, for example with respect to the projectionsystem. Any use of the terms “reticle” or “mask” herein may beconsidered synonymous with the more general term “patterning device.”

The term “patterning device” used herein should be broadly interpretedas referring to any device that can be used to impart a radiation beamwith a pattern in its cross-section such as to create a pattern in atarget portion of the substrate. It should be noted that the patternimparted to the radiation beam may not exactly correspond to the desiredpattern in the target portion of the substrate, for example if thepattern includes phase-shifting features or so called assist features.Generally, the pattern imparted to the radiation beam will correspond toa particular functional layer in a device being created in the targetportion, such as an integrated circuit.

The patterning device may be transmissive or reflective. Examples ofpatterning devices include masks, programmable mirror arrays, andprogrammable LCD panels. Masks are well known in lithography, andinclude mask types such as binary, alternating phase-shift, andattenuated phase-shift, as well as various hybrid mask types. An exampleof a programmable mirror array employs a matrix arrangement of smallmirrors, each of which can be individually tilted so as to reflect anincoming radiation beam in different directions. The tilted mirrorsimpart a pattern in a radiation beam, which is reflected by the mirrormatrix.

The term “projection system” used herein should be broadly interpretedas encompassing any type of projection system, including refractive,reflective, catadioptric, magnetic, electromagnetic and electrostaticoptical systems, or any combination thereof, as appropriate for theexposure radiation being used, or for other factors such as the use ofan immersion liquid or the use of a vacuum. Any use of the term“projection lens” herein may be considered as synonymous with the moregeneral term “projection system.”

As here depicted, the apparatus is of a reflective type (e.g., employinga reflective mask). Alternatively, the apparatus may be of atransmissive type (e.g., employing a transmissive mask).

The lithographic apparatus may be of a type having two (dual stage) ormore substrate tables (and/or two or more mask tables). In such“multiple stage” machines the additional tables may be used in parallel,or preparatory steps may be carried out on one or more tables while oneor more other tables are being used for exposure.

The lithographic apparatus may also be of a type wherein at least aportion of the substrate may be covered by a liquid having a relativelyhigh refractive index, e.g., water, so as to fill a space between theprojection system and the substrate. An immersion liquid may also beapplied to other spaces in the lithographic apparatus, for example,between the mask and the projection system. Immersion techniques arewell known in the art for increasing the numerical aperture ofprojection systems. The term “immersion” as used herein does not meanthat a structure, such as a substrate, must be submerged in liquid, butrather only means that liquid is located between the projection systemand the substrate during exposure.

Referring to FIG. 1, the illuminator IL receives a radiation beam from aradiation source SO. The source and the lithographic apparatus may beseparate entities, for example when the source is an excimer laser. Insuch cases, the source is not considered to form part of thelithographic apparatus and the radiation beam is passed from the sourceSO to the illuminator IL with the aid of a beam delivery system BDcomprising, for example, suitable directing mirrors and/or a beamexpander. In other cases the source may be an integral part of thelithographic apparatus, for example when the source is a mercury or tinbased lamp. The source SO and the illuminator IL, together with the beamdelivery system BD if required, may be referred to as a radiationsystem.

The illuminator IL may comprise an adjuster AD for adjusting the angularintensity distribution of the radiation beam. Generally, at least theouter and/or inner radial extent (commonly referred to as σ-outer andσ-inner, respectively) of the intensity distribution in a pupil plane ofthe illuminator can be adjusted. In addition, the illuminator IL maycomprise various other components, such as an integrator IN and acondenser CO. The illuminator may be used to condition the radiationbeam, to have a desired uniformity and intensity distribution in itscross-section.

A masking device, which defines the area on the patterning means that isilluminated, may be included in the illuminator IL. The masking devicemay comprise a plurality of blades, for example four, whose positionsare controllable, e.g., by actuators such as stepper motors, so that thecross-section of the beam may be defined. It should be noted that themasking device need not be positioned proximate the patterning means butin general will be located in a plane that is imaged onto the patterningmeans (a conjugate plane of the patterning means). The open area of themasking means defines the area on the patterning means that isilluminated but may not be exactly the same as that area, e.g., if theintervening optics have a magnification different than 1.

FIG. 2 depicts an exemplary beam interceptor which is comprised in amasking device according to an embodiment of the invention. The beaminterceptor 210, comprises opaque blades 211, 212, 213, 214 that arearranged to intercept part of the radiation beam B. The blades 211, 212,213, 214 manipulate the size and shape of the exposed projection beam Bon the mask MA and accordingly on the target portions C. The movementand positioning of the blades 211, 212, 213, 214 is controlled by acontrol system 220. If a projected target portion C is not fullypositioned on the substrate W, the control system 220 is arranged todefine a new size for this particular target portion C and actuate thebeam interceptor 210 accordingly.

The patterning device (e.g., mask MA) is held on the support structure(e.g., mask table MT) and is patterned by the patterning device. Themask MA can be clamped to the mask table MT on both surfaces of themask. By clamping the mask MA on both surfaces, the mask can besubjected to large accelerations without slipping or deformation. Theclamping, or holding force may be applied using thin membranes, whichfurther prevent deformation of the mask. By the clamp, a normal forcebetween adjacent surfaces of the mask and the mask table MT isgenerated, resulting in a friction between contacting surfaces of themask and the mask table. The clamping force to the surfaces of the maskMA may be generated using HV electrostatic or mechanical clampingtechniques.

The radiation beam B is incident on the patterning device (e.g., maskMA). Having traversed the mask MA, the radiation beam B passes throughthe projection system PS, which focuses the beam onto a target portion Cof the substrate W. With the aid of the second positioner PW andposition sensor IF2 (e.g., an interferometric device, linear encoder orcapacitive sensor), the substrate table WT can be moved accurately,e.g., so as to position different target portions C in the path of theradiation beam B. Similarly, the first positioner PM and anotherposition sensor IF1 can be used to accurately position the mask MA withrespect to the path of the radiation beam B, e.g., after mechanicalretrieval from a mask library, or during a scan. In general, movement ofthe mask table MT may be realized with the aid of a long-stroke module(coarse positioning) and a short-stroke module (fine positioning), whichform part of the first positioner PM. Similarly, movement of thesubstrate table WT may be realized using a long-stroke module and ashort-stroke module, which form part of the second positioner PW. In thecase of a stepper (as opposed to a scanner) the mask table MT may beconnected to a short-stroke actuator only, or may be fixed. Mask MA andsubstrate W may be aligned using mask alignment marks M1, M2 andsubstrate alignment marks P1, P2. Although the substrate alignment marksas illustrated occupy dedicated target portions, they may be located inspaces between target portions (these are known as scribe-lane alignmentmarks). Similarly, in situations in which more than one die is providedon the mask MA, the mask alignment marks may be located between thedies.

The depicted apparatus could be used in at least one of the followingmodes:

1. In step mode, the mask table MT and the substrate table WT are keptessentially stationary, while an entire pattern imparted to theradiation beam is projected onto a target portion C at one time (i.e., asingle static exposure). The substrate table WT is then shifted in the Xand/or Y direction so that a different target portion C can be exposed.In step mode, the maximum size of the exposure field limits the size ofthe target portion C imaged in a single static exposure. The clampingforce to the surfaces of the wafer may be generated using HVelectrostatic or mechanical clamping techniques.

2. In scan mode, the mask table MT and the substrate table WT arescanned synchronously while a pattern imparted to the radiation beam isprojected onto a target portion C (i.e., a single dynamic exposure). Thevelocity and direction of the substrate table WT relative to the masktable MT may be determined by the (de-) magnification and image reversalcharacteristics of the projection system PS. In scan mode, the maximumsize of the exposure field limits the width (in the non-scanningdirection) of the target portion in a single dynamic exposure, whereasthe length of the scanning motion determines the height (in the scanningdirection) of the target portion.

3. In another mode, the mask table MT is kept essentially stationaryholding a programmable patterning device, and the substrate table WT ismoved or scanned while a pattern imparted to the radiation beam isprojected onto a target portion C. In this mode, generally a pulsedradiation source is employed and the programmable patterning device isupdated as required after each movement of the substrate table WT or inbetween successive radiation pulses during a scan. This mode ofoperation can be readily applied to maskless lithography that utilizesprogrammable patterning device, such as a programmable (MEMS) mirrorarray of a type as referred to above.

Combinations and/or variations on the above described modes of use orentirely different modes of use may also be employed.

EP Patent No. 1 056 162 B1, which is incorporated by reference herein inits entirety, discloses a device for controlling an electric field. Thedevice makes use of capacitive field control and geometrical fieldcontrol. The capacitive field control comprises a plurality ofcapacitive layers arranged substantially concentrically between an innerlive conductor and an outer ground potential. The geometrical fieldcontrol comprises a stress cone, which is arranged in electrical contactground potential. However, arcing may still occur from the cables to anearby conductor. Arcing of this kind is a particular problem whenelectrical cables are connected in a system at low pressures. In orderto overcome this problem U.S. Pat. No. 6,485,331 B1, which isincorporated by reference herein in its entirety, discloses a connectionsystem for electrical cables, which operate under vacuum and carry highvoltage electric pulses or currents. This connection system comprises agrounded outer metal shell connected to the metal sheathes of the cablesand a dielectric insulating sleeve and confines the electric fieldsinside the cable sheathes, such that no electric fields occur outsidethe cable. The insulating sheath and sleeve enclose the cables to beconnected. The system is fitted with seals to form a sealed cavitybetween insulating sleeves of the cables and the insulating sheath. Thisensures that the insulators of the connection system remain immersed ina gas atmosphere even when part of the connection system is in a vacuum.This is designed to reduce arcing along the surfaces of insulatorjunctions of the connection systems. However, it is difficult to preventleaks in such a system. Any leaks in the interconnect system increasethe possibility of arcing, even over long creepage paths.

Embodiments of the present invention provide the first positioner PM,the second positioner PW, the motors that control any blades that may becomprised in the masking device and any clamps that may be comprised inthe lithographic projection apparatus are powered by a high voltagepower supply. High voltage is taken to mean that the power supplyproduces an output of the order of hundreds or thousands of volts. In anembodiment, the output of the power supply is greater than 100V, greaterthan 200V, greater than 500V, greater than 1000V, greater than 2000V,greater than 5000V.

FIGS. 3 a and 3 b each show an exemplary actuation system 300 in alithographic apparatus according to one embodiment of the presentinvention. The actuation system 300 comprises an actuator module 320, apower transmission module 340 and a power source module 360. The powersource module 360 supplies electrical power to the actuator module 320via the power transmission module 340.

In FIG. 3 a the motors 322 a comprise two three-phase motors.Consequently the power source module 360 provides a three-phase sourcevia two power amplifiers 364, each fed from power supply 362. Equallythe power transmission module 340 comprises cabling 368 a forthree-phase power. FIG. 3 b differs only in that there are now threesingle-phase motors 322 b, each fed by three single-phase poweramplifiers 364 via single-phase cabling 368 b. The FIG. 3 a systemapplies to the PWM 3-phase AC application and the FIG. 3 b systemapplies for a PWM DC supplied application. A multi-phase steppingactuator system can be applied in a similar way.

The actuator module 320 may be located in a low pressure environment,such as in a vacuum environment. The actuator module 320 includeselectrical motors 322 a, 322 b and a number of first sets of cables 324a, 324 b. Each first set of cables 324 a, 324 b is configured to connectto one of the electrical motors 322 a, 322 b at one end. In the exampleof FIG. 3 a there are two sets, each comprising three cables(three-phase), and in the example of FIG. 3 b there are three sets, eachcomprising two cables (single-phase).

FIG. 4, depicts the structure of the cables which make up the first setsof cables 324 a, 324 b. Each cable is comprised of a center conductor326, surrounded by a layer of insulator 327 and an outer layercomprising a conductive shield 328, such as a Paschen shield. The shield328 of the cables 324 is grounded to prevent corona discharge, usuallyby being connected to a chassis ground of the electrical motor 322.Therefore, the potential of the shield 328 of the cables 324 is zero.

Returning to FIGS. 3 a and 3 b, the chassis ground of the electricalmotors 322 form part of a network of wires and conductive structuralparts of the actuator system 300, such as the enclosure of theelectrical motor 322, all of which are connected to a protective earth,PE. This protective earth network is depicted in the figures by theblack dotted lines. None of the conductive parts of the electrical motor322 are galvanically connected to protective earth, as a parasiticcapacitance between the conductive parts and the enclosure of theelectrical motor 322 exists.

In one exemplary embodiment, the electrical motors 322 are implementedas actuators in a lithographic apparatus, for example actuating asubstrate table for positioning of the substrate table, the reticleclamp or the shutter blades.

The power source module 360 and power transmission module 340 eachinclude second sets of cables 368, which match the first sets of cables324 in their configuration and are for joining thereto, so as that poweris conveyed from the power source module 360, via the power transmissionmodule 340, to the actuator module 320. As these cables do not reside ina low-pressure atmosphere, they do not require any “corona” shielding,and are therefore of a more conventional design, each comprising asingle insulated conductor. Inside the power source module 360, each ofthese second sets of cables 368 is connected to a power amplifier 364via a multi-wire common-mode choke 365.

In the exemplary system 300, there is provided a common-mode returncircuit, shown bolder than the other cables in FIGS. 3 a and 3 b. Thiscomprises the shields 328 of each cable of the first set of cables 324in the low pressure actuation module and dedicated common-mode returncables 369 in the power source module 360 and power transmission module340. These dedicated common-mode return cables 369 are each comprised asan extra cable in each second set of cables 368.

Measurements have shown that the resolution of sensor systems isdeteriorated as a result of common-mode currents which interfere withsuch sensor systems. These common-mode currents arise from motioncontrol systems with electric motors (e.g., Wafer Stage), and is anissue for all machines with electric motors. It is therefore desirableto provide an extra common-mode return path to the power supply, ratherthan allow the common-mode current to flow through the chassis ground ofthe electrical motor. As a consequence of the extra common-mode returnpath by a conductive cable sheath or an extra “return” wire, thecommon-mode current flowing through the chassis ground of the electricalmotor 322 is made very small and therefore causes less interference withother electronic systems, such as a sensor system in a lithographicapparatus.

In the example shown, each dedicated common-mode return cable 369 isconnected to the power source 362 via the choke 365 and a divider 370,the latter to put the signal onto a common-mode of the power source 362.The choke 365 acts to control the path of the common-mode current, suchthat any common-mode component is carried by the common-mode returncable 369 and not through “chassis” ground. In one example, the choke365 has tightly coupled coils, such that the mutual inductance M of thechoke is substantially equal or at least similar to the self-inductanceL of the choke. Also, the inductance of the choke 365 can be much higherthan the total inductance of the cables in the actuator module 320, thepower transmission module 340 and the power source module 360. The useof shielded power cables can reduce the effective inductance[L_(eff)=2·(L−M)] of the cables being used, making the common-mode chokeusage more effective.

The fact that the conductive shielding of the cables 324 in the actuatormodule 320 is grounded at zero volts means that it can form a part ofthe common-mode return circuit, and therefore no dedicated common-modereturn cable is required in the actuator module, the cable shieldingtaking its place. In one example, the common-mode return for each motor322 is comprised of the shielding of all three/both (depending onphase-type) cables comprised in a set, in parallel. The concept forusing the extra return wire (as wire or cable sheath) can also be usedwith multi-phase stepping motor applications.

The depicted arrangement requires an electric feed-through 400 to carryboth the current source and the common-mode return through the wall ofthe actuator module and into the low pressure atmosphere. As such thefeed-through needs to be hermetically sealed, while not only connectingeach cable of sets 324 to the corresponding cable of sets 368, but alsoconnecting the shielding 328 of the cables 324 to a dedicatedfeed-through 400 for connection to the dedicated common-mode return wire369. As each shield in a set of cables 324 is being used in parallel,the feed-through should connect all the shields in a set to thededicated common-mode return wire 369. The return wire applied to eachof the actuators is driven separately, even when driven from a singlemotion driver. In case actuators are used in series, the return wireshall be applied in parallel to the actuator supply wires while makingcontact to each and every actuator in that “actuator chain.”

FIGS. 5 a (isometric) and FIG. 5 b (cross-section) both show a suitablefeed-through connector 400 for passing the power source through thevacuum wall 410. A male connector is shown, although the same principlescan equally be applied to a female connector. In this specificembodiment, feed-through connector 400 comprises six main feed-throughconductors 410, each one for connection of a cable from the first set ofcables to a cable from the second set of cables, and three auxiliaryfeed-through conductors 420, for the common-mode return circuit. Thefeed-through on the low pressure side (top in FIGS. 5 a and 5 b)comprises a plug 430 with main pins 440, each one of which iselectrically connected to, and extends, a main feed-through conductor410. Around each of these pins 440 is insulation 450, similar to that ofthe main plug body. Surrounding this insulation 450 is a conductivelayer 460. When cables of the first set are plugged into the connector400, their shielding will be electrically connected (either directly orvia an intermediary conductor in the cable termination using forexample, an electrical connector as disclosed in WO 2010/121844, whichis incorporated by reference herein in its entirety, to this conductivelayer 460.

FIGS. 6 a and 6 b show a horizontal cross section through thefeed-through connector (on the vacuum side) so as to illustrate how thecommon-mode signal is fed through the vacuum chamber wall 470. This isdone via the auxiliary feed-through conductors 420. The feed-throughconnector 400 in this embodiment is specifically arranged to be usablein both actuation systems illustrated in FIG. 3 a and FIG. 3 b. This isdone by providing channels 500 between the outer conductive layer 460 ofthe main feed-through conductors 410/pins 440, and the auxiliaryfeed-through conductors 420. These channels allow the location ofconductive springs 510 a, 510 b. Conductive spring 510 a is particularlydesigned for the PWM 3-phase actuation system illustrated in FIG. 3 a,while conductive spring 510 b is designed for the PWM DC actuationsystem illustrated in FIG. 3 b.

In FIG. 6 a, the pin 510 a effectively connects together the shieldingof one set of three cables carrying the three-phase power, and one ofthe auxiliary feed-through conductors 420. In this arrangement, one ofthe auxiliary feed-through conductors 420 is unused. As with the exampleshown in FIG. 3 a, by using two springs 510 a, the feed-through 400 canconnect two sets of three-phase power sources to power two three-phasemotors.

In FIG. 6 b, each pin 510 b effectively connects together the shieldingof one set of two cables carrying single-phase power, and one of theauxiliary feed-through conductors 420. As with the example shown in FIG.3 b, by using three springs 510 b, the feed-through 400 can connectthree sets of single-phase power sources to power three single-phasemotors.

Clearly this specific pin arrangement is an example, and otherarrangements can be envisaged depending on the requirements of thesystem.

It should also be noted that the actuation system 300 described hereinaddresses the issue of magnetic stray field that results from the motorcables, such as the first plurality of cables 324 of the actuator module320. This is because, for each of the first plurality of cables 324, thecurrent in the center conductor 326 is equal but opposite to the currentin the shield 328, this results in a net magnetic field equal to zero.

The above described embodiments of actuation systems 300 of the presentinvention are suitable for use in a lithographic apparatus to move orposition a mask table or a substrate table. Additionally, embodiments ofthe present invention may be used to move or position any beaminterceptor 210 (such as a blade) or provide power to any clamp (e.g.,an electrostatic clamp) used to fix a mask or a substrate to a tablethat may form part of a lithographic apparatus. However, the actuationsystem according to embodiments of the present invention is not limitedto use as part of a lithographic apparatus. The actuation system isapplicable in other situations where an actuator is located in lowpressure environments and the electrical cables carry high voltages inthe low pressure environments.

Although specific reference may be made in this text to the use oflithographic apparatus in the manufacture of ICs, it should beunderstood that the lithographic apparatus described herein may haveother applications, such as the manufacture of integrated opticalsystems, guidance and detection patterns for magnetic domain memories,flat-panel displays, liquid-crystal displays (LCDs), thin film magneticheads, etc. The skilled artisan will appreciate that, in the context ofsuch alternative applications, any use of the terms “wafer” or “die”herein may be considered as synonymous with the more general terms“substrate” or “target portion,” respectively. The substrate referred toherein may be processed, before or after exposure, in for example atrack (a tool that typically applies a layer of resist to a substrateand develops the exposed resist), a metrology tool and/or an inspectiontool. Where applicable, the disclosure herein may be applied to such andother substrate processing tools. Further, the substrate may beprocessed more than once, for example in order to create a multi-layerIC, so that the term substrate used herein may also refer to a substratethat already contains multiple processed layers.

Although specific reference may have been made above to the use ofembodiments of the invention in the context of optical lithography, itwill be appreciated that the invention may be used in otherapplications, for example imprint lithography, and where the contextallows, is not limited to optical lithography. In imprint lithography,topography in a patterning device defines the pattern created on asubstrate. The topography of the patterning device may be pressed into alayer of resist supplied to the substrate whereupon the resist is curedby applying electromagnetic radiation, heat, pressure or a combinationthereof. The patterning device is moved out of the resist leaving apattern in it after the resist is cured.

The terms “radiation” and “beam” used herein encompass all types ofelectromagnetic radiation, including ultraviolet (UV) radiation (e.g.,having a wavelength of or about 365, 355, 248, 193, 157 or 126 nm) andextreme ultra-violet (EUV) radiation (e.g., having a wavelength in therange of 5-20 nm), as well as particle beams, such as ion beams,electron or X-ray beams.

The term “lens,” where the context allows, may refer to any one orcombination of various types of optical components, includingrefractive, reflective, magnetic, electromagnetic and electrostaticoptical components.

The descriptions above are intended to be illustrative, not limiting.Thus, it will be apparent to one skilled in the art that modificationsmay be made to the invention as described without departing from thescope of the claims set out below.

It is to be appreciated that the Detailed Description section, and notthe Summary and Abstract sections, is intended to be used to interpretthe claims. The Summary and Abstract sections may set forth one or morebut not all exemplary embodiments of the present invention ascontemplated by the inventor(s), and thus, are not intended to limit thepresent invention and the appended claims in any way.

The present invention has been described above with the aid offunctional building blocks illustrating the implementation of specifiedfunctions and relationships thereof. The boundaries of these functionalbuilding blocks have been arbitrarily defined herein for the convenienceof the description. Alternate boundaries can be defined so long as thespecified functions and relationships thereof are appropriatelyperformed.

The foregoing description of the specific embodiments will so fullyreveal the general nature of the invention that others can, by applyingknowledge within the skill of the art, readily modify and/or adapt forvarious applications such specific embodiments, without undueexperimentation, without departing from the general concept of thepresent invention. Therefore, such adaptations and modifications areintended to be within the meaning and range of equivalents of thedisclosed embodiments, based on the teaching and guidance presentedherein. It is to be understood that the phraseology or terminologyherein is for the purpose of description and not of limitation, suchthat the terminology or phraseology of the present specification is tobe interpreted by the skilled artisan in light of the teachings andguidance.

The breadth and scope of the present invention should not be limited byany of the above-described exemplary embodiments, but should be definedonly in accordance with the following claims and their equivalents.

1. An actuator system comprising: an actuator module comprising at leastone actuator and actuator cables configured to connect the at least oneactuator to the outside of the actuator module; a power supply forproviding power to the at least one actuator; and transmission cablesfor connecting the power source to the actuator cables, wherein there isprovided a common-mode signal return conductor from the at least oneactuator module to the power supply.
 2. The actuator system as claimedin claim 1, comprising a plurality of actuators and a separatecommon-mode signal return conductor for each actuator
 3. The actuatorsystem as claimed in claim 1, wherein: a low pressure is maintained inthe actuator module and the actuator cables are provided with groundedelectrically conductive shielding so as to prevent discharge; and thegrounded electrically conductive shielding comprises part of thecommon-mode signal return conductor.
 4. The actuator system as claimedin claim 3, wherein the grounded electrically conductive shielding of aset of actuator cables is used in parallel to provide the part of acommon-mode signal return conductor, the set of actuator cables beingoperable to provide a power source to a single actuator, and providesthe part of a common-mode signal return conductor only for the singleactuator.
 5. The actuator system as claimed in claim 4, furthercomprising a feed-through connection configured to connect the actuatorcables to the transmission cables, while providing a feed-through forthe common-mode signal return conductor through the actuator modulewall.
 6. The actuator system as claimed in claim 1, further comprisingfor each actuator, a dedicated conductor within the transmission cablesfor providing part of the common-mode signal return conductor.
 7. Theactuator system as claimed in claim 1, further comprising a chokebetween the power supply and each of the transmission cables and thecommon-mode signal return conductor, the choke being operable to controlthe path of the common-mode current such that any common-mode componentis carried by the common-mode signal return conductor.
 8. The actuatorsystem as claimed in claim 7, wherein the mutual inductance of the chokeis substantially equal to self-inductance of the choke, and theinductance of the choke is at least an order of magnitude higher thanthat of the total inductance of the cables comprised in the system.
 9. Afeed-through connection comprising: one or more main feed-throughconductors, each of which is configured at each end to connect to anelectrical cable; and one or more auxiliary feed-through conductors,each of which is insulated from the one or more main feed-throughconductors, the feed-through connection being configured at one end toprovide for an electrically conductive path from an electricallyconductive shielding of at least one of the electrical cables to atleast one of the one or more auxiliary feed-through conductors.
 10. Thefeed-through connection as claimed in claim 9, wherein the one or moreauxiliary feed-through conductors are held at ground voltage.
 11. Thefeed-through connection as claimed in claim 9, further comprising: aplurality of both the main feed-through conductors and the auxiliaryfeed-through conductors; and a locating device configured to locate alinking conductor, the linking conductor being operable to provide forthe electrically conductive path from the electrically conductiveshielding of a set of cables to one of the auxiliary feed-throughconductors, the set of cables comprising the power lines of a singlepower supply.
 12. The feed-though connection as claimed in claim 11,wherein the locating device is able to locate two different types ofconductor, a first type for connecting the shielding of pairs of cablesto one of the auxiliary feed-through conductors, and a second type forconnecting the shielding of three cables to one of the auxiliaryfeed-through conductors.
 13. The feed-through connection as claimed inclaim 12, comprising six main feed-through conductors and threeauxiliary feed-through conductors, such that they can be linked by threelinking conductors of the first type, to feed through three single-phasepower supplies or two linking conductors of the second type, to feedthrough two three-phase power supplies, while also providing acommon-mode return signal path for each power supply via theelectrically conductive shielding, linking conductors and the auxiliaryfeed-through conductors.
 14. A lithographic apparatus, comprising: asubstrate table configured to hold a substrate; a support constructed tosupport a patterning device, the patterning device being capable ofimparting the radiation beam with a pattern in its cross-section to forma patterned radiation beam; and an actuation system comprising: anactuator module comprising at least one actuator and actuator cablesconfigured to connect the at least one actuator to the outside of theactuator module; a power supply for providing power to the at least oneactuator; and transmission cables for connecting the power source to theactuator cables, wherein there is provided a common-mode signal returnconductor from the at least one actuator module to the power supplywherein the actuating system is configured to actuate the support, thesubstrate table, and/or any other feature of the lithographic apparatus.15. The lithographic apparatus as claimed in claim 14, furthercomprising: an illumination system configured to condition a radiationbeam; a projection system configured to project the patterned radiationbeam onto a target portion of the substrate; and a beam interceptorconfigured to intercept a portion of a part of the projection beam;wherein the actuation system is further configured to actuate the beaminterceptor.